In recent years, liquid crystal display (LCD) devices have been widely used as flat panel displays in various fields. However, there still are significant challenges in the LCD devices. For example, contrast and displayed colors vary significantly depending on the viewing angle. Since the LCD devices require a light source such as a backlight, it is difficult to reduce power consumption. Moreover, reduction in thickness and weight of the LCD devices is limited. Another challenge for the LCD devices is to use the LCD devices in flexible display applications.
Recently, self light-emitting organic EL display devices using organic electroluminescence (organic EL) elements have been expected as an alternative display device to the LCD devices. The organic EL element is an element configured so that organic molecules forming an organic EL layer emit light in response to a current applied to the organic EL layer interposed between an anode and a cathode. Since the organic EL display devices using the organic EL elements are of the self light-emitting type, the organic EL display devices are advantageous in terms of reduction in thickness, weight, and power consumption, and also have a wide viewing angle. Thus, the organic EL display devices have received considerable attention as a candidate for the next-generation flat panel displays. There is also a possibility that the organic EL display devices may be superior to the LCD devices in flexible display applications as well. Taking advantage of their small thickness and wide viewing angle, the organic EL display devices have been actually increasingly used in practical applications as main displays of portable audio players or mobile phones.
This organic EL display device has a plurality of organic EL elements arranged in a predetermined pattern, and each of the plurality of organic EL elements includes a first electrode formed on an insulating substrate, an organic EL layer having a light emitting layer formed on the first electrode, and a second electrode formed on the organic EL layer. The organic EL element is provided with an edge cover in a region other than a light emitting region in order to prevent short-circuit between the first and second electrodes. Thin film transistors (TFTs) are provided on the substrate, and a planarizing film (an interlayer film) is provided in order to planarize the substrate surface and to provide insulation.
The planarizing film is made of an organic resin material such as an acrylic resin, in view of the dielectric constant and the film thickness, easiness of planarization, and high controllability of both patterning and the taper angle at pattern ends.
However, the organic resin material such as the acrylic resin tends to accumulate water therein, as compared to a material made of an inorganic component. Moreover, the acrylic resin is resistant to a temperature of up to about 250° C. Thus, even if baking is performed at 250° C. or less in the manufacturing process, it is difficult to sufficiently remove water from the planarizing film made of the acrylic resin. Accordingly, in the case where the planarizing film is made of the organic resin material, water leaks from the planarizing film, and reaches the electrodes and the organic EL layer of the organic EL element, thereby damaging the peripheral portions of the electrodes and the organic EL layer. As a result, luminance decreases in the degraded portions, causing uneven light emission.
As a solution to this problem, organic EL display devices have been proposed which are configured to prevent such damage caused by the water. More specifically, for example, an organic EL display device has been proposed which includes an organic resin film placed between a first electrode and an organic EL layer and having a low hygroscopic property, and an organic resin film placed at the boundary of the first electrode and having a relatively high hygroscopic property as compared to the organic resin film having a low hygroscopic property. This configuration can block the water leaking from the planarizing film to the organic EL layer, whereby degradation of the organic EL element is suppressed, and an organic EL display device that is less likely to be degraded can be implemented (e.g., Patent Document 1).
As another example, an organic EL display device has also be disclosed in which a first inorganic insulating film is formed in a layer below a planarizing film, and a second inorganic insulating film is formed in a layer above the planarizing film, so that the lower, upper, and side surfaces of the planarizing film are covered by the first inorganic insulating film and the second inorganic insulating film. According to the disclosure, this configuration can prevent absorption of water by the planarizing film during the manufacturing process, whereby problems resulting from absorption of water by the planarizing film can be prevented (see, e.g., Patent Document 2).